1. Field of the Invention
The present invention relates to a clay mixing apparatus for mixing clay.
2. Description of the Related Art
Conventionally, there has been used a clay mixing apparatus suitable for mixing clay to manufacture a piece of earthenware. If an air remains within the clay for the manufacture of earthenware, crack or breakage may occur in a biscuit firing step. In light of this, a variety of studies has been made in the field of clay mixing apparatus. For example, Japanese Patent Application Publication No. H7-214537 discloses a clay mixing apparatus in which an air is discharged from a mixing chamber by virtue of a vacuum suction device. Referring to FIG. 6 of Japanese Patent Application Publication No. H7-214537, a suction pipe is arranged at the rear side of the top of a lid in order to efficiently circulate the clay.
U.S. Pat. No. 5,716,130 discloses a clay mixing apparatus in which a vacuum chamber is connected to a tubular vessel. A shaft is arranged to extend from the vacuum chamber toward the tubular vessel. The shaft is inserted into an opening of a wall existing between the vacuum chamber and the tubular vessel. A gap is left between the shaft and the wall. A plurality of blades is attached to the shaft. A helical portion is provided at the tip end of the shaft. The blades axially overlap with one another. In operation, materials are mixed within a mixing chamber as if the shaft rotates. After a specified time has lapsed, the vacuum chamber is evacuated through the opening of the wall. Then the shaft is rotated in the reverse direction, whereby the clay is extruded from an extruding and molding portion under the action of the helical portion.
Within the mixing chamber, the clay having an increased viscosity is mixed with a strong force. For that reason, the clay adheres to different areas within the mixing chamber. In order to prevent the clay from adhering to the opening for evacuation, there is a need to form the mixing chamber into an upwardly enlarged shape as in the clay mixing apparatus of Japanese Patent Application Publication No. H7-214537. In this structure, however, the size of the clay mixing apparatus grows larger. In case of the clay mixing apparatus disclosed in U.S. Pat. No. 5,716,130, it is necessary to install a complex mechanism around the shaft. In addition, it is impossible to readily remove the clay infiltrating into the vacuum chamber.
The clay, when stirred with large blades, is not finely cut. This makes it impossible to rapidly remove an air from the clay.
When extruding the mixed clay through the use of a helical screw, the clay is rotationally extruded under the influence of the rotation of the screw. As a consequence, the clay is extruded in a distorted state if a molding portion for molding the clay into a shape other than the circular shape is attached to the extrusion hole.